Microsoft Word won't take my product key

> I had to re-format my computer because of the worm virus
> that was going around and after downloading everything
> back onto my computer I am having a problem with
> microsoft word. I am trying to open it up to use it but
> it begins with wanting my user information. I try to
> type in my 25 character product key that is on the side
> of my computer and it will not accept it. It says that
> it is not valid. It said that it might be on the CD case
> also but the book that I have said that the sticker has
> been removed and I should get the number from the side of
> my tower. Am I getting the number from the wrong place.
> I am using the one that says Product Key. I of course
> can't get a hold of Dell, so I was hoping that somebody
> had an idea for me as to why this doesn't work. If you
> do, please reply! Thanks